Method of etching dual damascene structure

ABSTRACT

In an etching method for achieving a dual damascene structure by using at least one layer of a low-k film and at least one layer of a hard mask, a dummy film, which is ultimately not left in the dual damascene structure, is formed in at least one layer over the hard mask in order to prevent shoulder sag. By adopting this method, a dual damascene structure in which the extent of the shoulder sag at the hard mask is minimized can be achieved through etching.

BACKGROUND OF THE INVENTION

The present invention relates to an etching method that may be adoptedto achieve a dual damascene structure.

As higher integration in semiconductor integrated circuits is pursuedwith increasing vigor, rapid progress has been made in the field of thetechnology for manufacturing multilayered semiconductor devices inrecent years. It is necessary to form both trench wiring to connectelements arranged along the horizontal direction and via hole wiring toconnect elements arranged along the vertical direction whenmanufacturing a semiconductor device with a multilayer structure. Inrecent years, copper, due to its low resistance and outstandingantielectro-migration characteristics, is typically used as the wiringmaterial. An organic low-k (Low-dielectric-constant) material such asSiLK™ (product of Dow Chemical, U.S.), which assures a low dielectricconstant, is used as a layer insulating film material with a lowdielectric constant of 4 or lower relative to the dielectric constant ofquartz. Alternatively, an inorganic low-k material, such asfluorine-added silicon oxide (hereafter referred to as an FSG film) witha low dielectric constant, is used for the layer insulating material.

It is to be noted that a wiring pattern is formed with copper, withwhich a compound with a high vapor pressure cannot easily be formed, byadopting a so-called damascene structure with an embedded wiringachieved through metal CMP technology. In addition, semiconductorelements with a so-called dual damascene structure achieved bysimultaneously forming trench wiring for connecting the individualelements arranged along the horizontal direction and via wiring forconnecting the elements arranged along the vertical direction havebecome increasingly common recently. When creating such a dual damascenestructure, the insulating layer is etched by using a hard mask formedthrough patterning to form the trenches and the vias.

FIGS. 7 and 8 present an example of a process through which a dualdamascene structure is formed in the related art. As shown and FIG. 7A,an FSG layer 4 constituted of an inorganic low-k film is formed as alayer insulating film on top of an SiN layer 2 provided as a protectivefilm. Over the FSG layer 4, a SiLK™ layer 6 constituted of an organiclow-k film is formed and over the SiLK™ layer 6, an SiO₂ layer 8constituting a first hard mask and a silicon oxide nitride film(hereafter referred to as an SiON film) layer 10 constituting a secondhard mask are formed as hard mask layers to be used to form trenches andvias. Over the hard mask layers, a photoresist (PR) layer 12 having apattern to be used for trench formation is formed.

First, as shown in FIG. 7B, the SiON layer 10 constituting the secondhard mask is etched through a specific lithography process by using thephotoresist (PR) layer 12 for trench formation and thus, a trenchpattern is formed. Then, as shown in FIG. 7C, a photoresist (PR) layer14 for via formation is formed.

Next, as shown in the FIG. 7D, the SiO₂ layer 8 constituting the firsthard mask is etched through a specific lithography process by using thephotoresist (PR) layer 14 for via formation and thus, a via pattern isformed.

Then, using the hard mask for via formation formed in the precedingstep, the SiLK™ layer 6 constituted of an organic low-k film is etchedto form a via and the photoresist (PR) layer 14 is removed throughashing as shown in FIG. 7E.

Next, as shown in FIG. 7F, a trench pattern is formed at an Sio₂ layer 8constituting the first hard mask by using the trench pattern at the SiONlayer 10 formed as the second hard mask and also, vias are formed at theFSG layer 4 by using the via formed at the SiLK™ layer 6 a via pattern.

Next, as shown in FIG. 8A, the trench pattern at the SiO₂ layer 8constituting the first hard mask and the SiON layer 10 constituting thesecond hard mask is used to form a trench pattern at the SiLK™ layer 6.

Next, as shown in FIG. 8B, the SiN layer 2 is etched by using the viapattern at the FSG layer 4 to form through via holes. Thus, a dualdamascene structure is completed by forming the trenches and the viassimultaneously. Then, the wiring process is completed by embedding Cu ora metal containing Cu (not shown) into the trenches and the vias.

However, during a step in which a hard mask becomes exposed in theprocess described above, shoulder sag, whereby the shoulders of the hardmask are ground and the shoulder edges become tapered, tends to occurreadily. For instance, during the step shown in FIG. 7F, shoulder sagoccurs as shown in FIG. 9 at the SiO₂ layer 8 constituting the firsthard mask and the SiON layer 10 constituting the second hard mask whichhave become exposed due to over-etching after removing the photoresist(PR) layer 14.

The shoulder sag that occurs at the SiON layer 10 constituting thesecond hard mask, in particular, cannot be corrected through subsequentsteps and rather, the shoulder tends to become further ground throughetching in the subsequent steps. The shoulder sag occurring at the hardmask induces over-polishing (dishing) over densely patterned areasduring a post-processing step such as a CMP step, which, in turn, maylead to shorting of the wiring.

An object of the present invention, which has been completed byaddressing the problem discussed above, is to provide an etching methodfor achieving a dual damascene structure, through which the extent ofshoulder sag at a hard mask can be minimized.

SUMMARY OF THE INVENTION

In order to achieve the object described above, a first aspect of thepresent invention provides an etching method for achieving a dualdamascene structure by using at least one layer of a low-k film and atleast one layer of a hard mask, characterized in that a dummy filmconstituted of a material matching that constituting the hard mask,which will not ultimately be left in the dual damascene structures, isformed in at least one layer over the hard mask in order to preventshoulder sag. Through this method in which the dummy film instead of thehard mask becomes exposed during a step in which the hard mask would beexposed in the related art and thus, the dummy film is used as aprotective film, the extent of shoulder sag at the hard mask can beminimized. Furthermore, by covering the hard mask with the dummy filmconstituted of the same material used to form the hard mask, the low-kfilm (e.g., a SiLK™ layer) which has become exposed can be covered againand, as a result, the material such as SiLK™ constituting the low-k filmand the resist are not allowed to mix together. It is to be noted that,since this dummy film is ultimately removed, its presence does notaffect the finished dual damascene structure.

In this method, it is desirable to form the low-k film with twodifferent types of films which are etched by using different gases, andin such a case, the lower low-k film may be an inorganic low-k film andthe upper low-k film may be an organic low-k film. The inorganic low-kfilm may be constituted of, for instance, FSG, whereas the organic low-kfilm may be constituted of, for instance, SiLK™.

In addition, the hard mask may be formed over a single layer or twolayers. Preferably, such a hard mask should be constituted of SiON.Since an SiON film can be used as a reflection-reducing film as well, anadded advantage of sustaining dimensional stability during thelithography process is achieved. The dummy film may include a filmconstituted of the material with which the hard mask is formed, or itmay be constituted of SiON.

A second aspect of the present invention provides an etching method forachieving a dual damascene structure, through which vias are formed atan inorganic low-k film layer and trenches are formed at an organiclow-k film layer by etching the inorganic low-k film, the organic low-kfilm, a first hard mask and a second hard mask sequentially laminated ona lower wiring layer, comprising a first step in which a trench patternis formed at the second hard mask through a lithography process, asecond step in which a third hard mask is formed over the trench patternconstituted of the second hard mask, a third step in which a via patternis formed at the third hard mask and the first hard mask through alithography process, a fourth step in which vias are formed at theorganic low-k film by using the via pattern constituted of the thirdhard mask and the first hard mask, a fifth step in which the third hardmask is at least partially removed, a sixth step in which the remainingthird hard mask layer is removed, a trench pattern is formed at thefirst hard mask by using the trench pattern constituted of the secondhard mask and vias are formed at the inorganic low-k film by using thevias formed at the organic low-k film as a via pattern without alteringetching conditions and a seventh step in which trenches are formed atthe organic low-k film by using the trench pattern constituted of thefirst and second hard masks. In this method, even if shoulder sag occursat the third hard mask during the step in which it becomes exposed, ahard mask with no shoulder sag can be reformed by removing part of thethird hard mask. In addition, since the third hard mask functions as aprotective film, shoulder sag at the second hard mask can be minimized.

In this case, it is desirable to form the third hard mask as a dummyfilm that is not ultimately allowed to remain in the dual damascenestructure and includes a plurality of film layers. Then, the upper layerof the third hard mask can be removed through the fifth step and thelower layer of the third hard mask can be removed through the sixthstep. It is to be noted that the upper layer of the third hard mask maybe constituted of SiON, whereas the lower layer may be constituted of asilicon oxide film (hereafter referred to as “oxide”). The use of anSiON film which also functions as a reflection-reducing film achieves anadded advantage of sustaining dimensional stability during thelithography process.

In addition, a third aspect of the present invention provides an etchingmethod for achieving a dual damascene structure, through which vias areformed at an inorganic low-k film layer and trenches are formed at anorganic low-k film layer by etching the inorganic low-k film, theorganic low-k film, a first hard mask and a second hard masksequentially laminated on a lower wiring layer, comprising a first stepin which a trench pattern is formed at the second hard mask through alithography process, a second step in which a third hard mask is formedover the trench pattern constituted of the second hard mask, a thirdstep in which a via pattern is formed at the third hard mask and thefirst hard mask through a lithography process, a fourth step in whichvias are formed at the organic low-k film by using the via patternconstituted of the third hard mask and the first hard mask, a fifth stepin which the third hard mask layer is removed, a trench pattern isformed at the first hard mask by using the trench pattern constituted ofthe second hard mask and vias are formed at the inorganic low-k film byusing the vias formed at the organic low-k film as a via pattern withoutaltering etching conditions and a sixth step in which trenches areformed at the organic low-k film by using the trench pattern constitutedof the first and second hard masks. In addition, since the third hardmask functions as a protective film, shoulder sag at the second hardmask can be prevented. In this method, the third mask may be formed as adummy film which is ultimately not allowed to remain in the dualdamascene structure and includes a plurality of film layers.

A fourth aspect of the present invention provides an etching method forachieving a dual damascene structure, through which vias are formed atan inorganic low-k film layer and trenches are formed at an organiclow-k film layer by etching the inorganic low-k film, the organic low-kfilm and a first hard mask sequentially laminated on a lower wiringlayer, comprising a first step in which a trench pattern is formed atpart of the first hard mask through a lithography process, a second stepin which a second hard mask is formed over the trench pattern at thefirst hard mask, a third step in which a via pattern is formed at theremaining first hard mask and the second hard mask through a lithographyprocess, a fourth step in which vias are formed at the organic low-kfilm by using the via pattern constituted of the first and second hardmasks, a fifth step in which a trench pattern is formed by removing thesecond hard mask and etching the trench pattern portion of the firsthard mask, a sixth step in which vias are formed at the inorganic low-kfilm by using the vias formed at the organic low-k film as a via patternand a seventh step in which trenches are formed the organic low-k filmby using the trench pattern constituted of the first hard mask. Byadopting this method, in which a hard mask with no shoulder sag can bereformed by removing the second hard mask even if shoulder sag occurs atthe second hard mask during the step in which it becomes exposed, thesecond hard mask acts as a protective film to minimize the extent ofshoulder sag at the first hard mask.

A fifth aspect of the present invention provides an etching method forachieving a dual damascene structure, through which vias are formed atan inorganic low-k film layer and trenches are formed at an organiclow-k film layer by etching the inorganic low-k film, the organic low-kfilm and a first hard mask sequentially laminated on a lower wiringlayer, comprising a first step in which a trench pattern is formed atpart of the first hard mask through a lithography process, a second stepin which a second hard mask is formed over the trench pattern at thefirst hard mask, a third step in which a via pattern is formed at theremaining first hard mask and the second hard mask through a lithographyprocess, a fourth step in which vias are formed at the organic low-kfilm by using the via pattern constituted of the first and second hardmasks, a fifth step in which vias are formed at the inorganic low-k filmby using the vias formed at the organic low-k film as a via pattern, asixth step in which the second hard mask is removed, a seventh step inwhich a trench pattern is formed by etching the trench pattern portionof the first hard mask and an eighth step in which trenches are formedat the organic low-k film by using the trench pattern constituted of thefirst hard mask.

It is desirable to form the first and second hard masks of a singlematerial. In such a case, even if part of the first hard mask undergoinga process of partial etching becomes over-etched and the organic low-kfilm becomes exposed as a result, it is covered with the second hardmask constituted of the same material and thus, no mixing occurs. It isto be noted that the first and second hard mask should be preferablyconstituted of SiON. The use of SiON, which also acts as areflection-reducing film, achieves an added advantage of sustainingdimensional stability during the lithography process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates the structure of an etching apparatusin which the present invention may be adopted;

FIG. 2 shows steps executed in an etching method achieved in anembodiment;

FIG. 3 shows steps executed in the etching method achieved in theembodiment;

FIG. 4 shows steps executed in an etching method achieved in anembodiment;

FIG. 5 shows steps executed in the etching method achieved in theembodiment;

FIG. 6 presents a chart of the etching capabilities of different mixedgases for etching various films;

FIG. 7 shows steps executed in an etching method in the related art;

FIG. 8 shows steps executed in the etching method in the related art;and

FIG. 9 is a partial enlargement showing shoulder sag occurring at a hardmask.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is an explanation of preferred embodiments of the etchingmethod according to the present invention, given in reference to theattached drawings. It is to be noted that the same reference numeralsare assigned to members achieving substantially identical functions andstructural features in the following explanation and the attacheddrawings to preclude the necessity for a repeated explanation thereof.

First, the structure of a plane-parallel type plasma etching apparatusis briefly explained as an example of an etching apparatus in which theetching methods achieved in the embodiments may be adopted, in referenceto FIG. 1.

A processing chamber 104 is formed inside a processing container 102which is grounded for safety in an etching apparatus 100 in the figure,with a lower electrode 106 constituting a susceptor capable of movingup/down freely provided inside the processing chamber 104. At the top ofthe lower electrode 106, an electrostatic chuck 110 connected to ahigh-voltage DC source 108 is provided, and a substrate such as asemiconductor wafer (hereafter referred to as a “wafer”) W is placed onthe upper surface of the electrostatic chuck 110. An insulating focusring 112 is set around the wafer W placed on the lower electrode 106. Ahigh-frequency source 120 is connected to the lower electrode 106 via amatcher 118.

At the ceiling of the processing chamber 104 facing opposite the surfaceof the lower electrode 106 on which the substrate is placed, an upperelectrode 122 having numerous gas outlet holes 122 a is provided. Theupper electrode 122 and the processing container 102 are electricallyinsulated from each other by an insulator 123 provided between them. Ahigh-frequency source 121 which outputs plasma-generating high-frequencypower is connected to the upper electrode 122 via a matcher 119. A gassupply pipe 124 is connected with the gas outlet holes 122 a and aprocess gas supply system 126 is connected to the gas supply pipe 124. Agas supply source 136 from which the process gas is supplied via aswitching valve 132 and a flow-regulating valve 134 is connected to theprocess gas supply system 126.

Near the bottom of the processing container 102, an evacuating pipe 150communicating with an evacuating mechanism (not shown) is connected, andby engaging the evacuating mechanism in operation, the atmosphere insidethe processing chamber 104 can be maintained at a predetermined lowpressure level.

Next, the steps executed to form a dual damascene structure in a firstembodiment of the present invention by using the etching apparatusdescribed above are explained in reference to FIGS. 2 and 3. As shownand FIG. 2A, an FSG layer 204 constituted of an inorganic low-k film(with a film thickness of 500 nm) is formed as a layer insulating filmon top of an SiN layer 202 (with a film thickness of 50 nm), whichfunctions as a protective film. Over the FSG layer 204, a SiLK™ layer206 (with a film thickness of 400 nm) is formed as an organic low-kfilm. Over the SiLK™ layer 206, an SiO₂ layer 208 (with a film thicknessof 100 nm) constituting a first hard mask and an SiON layer 210 (with afilm thickness of 100 nm) constituting a second hard mask are formed ashard mask layers to be used to form trenches and vias and, over the hardmask layers, a photoresist (PR) layer 212 having a pattern to be usedfor the trench formation is formed.

First, as shown in FIG. 2B, the SiON layer 210 constituting the secondhard mask is etched and a trench pattern is formed through a specificlithography process executed by using the photoresist (PR) layer 212 fortrench formation (first step). The etching conditions under which thisstep is executed include, for instance, the pressure of the atmospherewithin the processing chamber set to 50 mT, the level of the powerapplied to the electrode set to 500 W and the flow rates of theindividual gases CH₂F₂, O₂ and Ar constituting the mixed gas set to 20sccm, 20 sccm and 100 sccm respectively.

After the remaining photoresist (PR) layer 212 is removed throughashing, a third hard mask is formed over the trench pattern constitutedof the second hard mask, as shown in FIG. 2C (second step). In thisembodiment, the third hard mask is a thin film constituted of twolayers, i.e., a lower oxide layer 214 (with a film thickness of lessthan 10 nm) and an upper SiON layer 216 (with a film thickness of lessthan 10 nm). While the oxide layer 214 and the SiON layer 216 may beformed through CVD (chemical vapor deposition), they may be formedthrough spin-coating as well. The oxide layer 214 and the SiON layer 216can be formed through the spin-coating by applying inorganic SOG with anextremely low viscosity at approximately 5000 rpm and allowing of theinorganic SOG thus applied to harden at 400° C. Then, as shown in FIG.2D a photoresist (PR) layer 218 for via formation is formed over thethird hard mask.

Next, as shown in FIG. 2E, the oxide layer 214 and the SiON layer 216constituting the third hard mask and the SiO₂ layer 208 constituting thefirst hard mask are etched to form a via pattern through a specificlithographic process executed by using the photoresist (PR) layer 218for via information (third step). This step is executed under etchingconditions which include, for instance, the pressure of the atmospherewithin the processing chamber set to 40 mT, the level of power appliedto the electrodes set to 1500 W and the flow rates of CF₄, O₂ and Arconstituting the mixed gas set to 80 sccm, 20 sccm and 160 sccmrespectively.

Then, by using the via hard mask constituted of the third hard mask andthe first hard mask, which has been formed in the third step, the SiLK™layer 206 constituted of an organic low-k film is etched and vias areformed at the SiLK™ layer 206 and the photoresist (PR) layer 218 isremoved through ashing, as shown in FIG. 2F (fourth step). This step isexecuted under etching conditions which include, for instance, thepressure of the atmosphere within the processing chamber set to 100 mT,the level of the power applied to the electrodes set to 1000 W and theflow rates of N₂ and H₂ constituting the mixed gas set to 100 sccm and300 sccm respectively. After the photoresist (PR) layer 218 is removedduring the step, shoulder sag may occur at the exposed third hard maskdue to over-etching.

Accordingly, the upper layer of the third hard mask, i.e., the SiONlayer 216, where the shoulder sag has occurred is removed throughisotropic etching, as shown in FIG. 3A (fifth step). This etchingprocess should be executed at the lowest possible ion energy level andunder conditions which achieves a high selection ratio relative to SiO₂,or the process should be executed through wet etching. Since the lowerlayer, i.e., the oxide layer 214, is still present after the upper SiONlayer 216 is removed, a third hard mask with no shoulder sag isreformed.

Next, as shown in FIG. 3B, the lower layer of the third hard mask, i.e.,the oxide layer 214, is removed, a trench pattern is formed at the SiO₂layer 208 constituting the first hard mask by using the trench patternat the SiON layer 210 constituting the second hard mask and vias areformed at the FSG layer 204 by using the vias formed at the SiLK™ layer206 as a via pattern under etching conditions which remain unchangedthroughout the step (sixth step). The etching conditions include, forinstance, the pressure of the atmosphere within the processing chamberset to 45 mT, the level of the power applied to the electrodes set to1500 W and the flow rates of the C₄F₈, CO and Ar constituting the mixedgas set to 12 sccm, 225 sccm and 400 sccm respectively.

Then, as shown in FIG. 3C, a trench pattern is formed at the SiLK™ layer206 by using the trench pattern at the SiO₂ layer 208 constituting thefirst hard mask and at the SiON layer 210 constituting the second hardmask (seventh step).

Next, as shown in FIG. 3D, the SiN layer 202 is etched by using the viapattern at the FSG layer 204 to achieve a through via hole. This processshould be executed under etching conditions which include, for instance,the pressure of the atmosphere within the processing chamber set to 30mT, the level of the power applied to the electrodes set to 500 W andthe flow rates of CH₂F₂, O₂ and Ar constituting the mixed gas set to 20sccm, 20 sccm and 100 sccm respectively. Through the steps describedabove a dual damascene structure having trenches and vias formedsimultaneously therein is completed. Then, a wiring step is completed byembedding Cu or a metal containing Cu (not shown) in the trenches andthe vias.

It is to be noted that FIG. 6 presents a chart of the relative etchingcapabilities of the various mixed gases used in the etching processesfor processing the individual films. ◯, Δ and X in the chartrespectively indicate high etching capability, intermediate etchingcapability and low etching capability. While a mixed gas marked X doesnot have any chemical etching capability, it does have a degree ofphysical etching capability.

As described above, by forming the third hard mask over the second hardmask for trench pattern formation as a dummy film which is ultimatelynot left in the dual damascene structure, the first and second hardmasks that become exposed in the etching methods in the related art areprotected and thus, it becomes possible to prevent shoulder sag fromoccurring at these hard masks. In addition, the 2-layer structureadopted in the third hard mask allows a hard mask with no shoulder sagto be reformed by removing the upper layer of the third hard mask whereshoulder sag has occurred during the process. These advantages willprove even more effective under circumstances in which the adverseeffects of the shoulder sag is more significant in the related art,i.e., when the width of the trenches is approximately 0.18 μm or smallerand the via diameter is approximately 0.13 μm or smaller. In addition,since the SiON layer constituting the upper stratum of the third hardmask also functions as a reflection-reducing film, there is an addedadvantage of sustaining dimensional stability during the lithographyprocess.

It is to be noted that all the remaining SiON layer 216 may be removedtogether with the lower oxide layer 214 in the sixth step with only partof the SiON layer 216 or none of the SiON layer 216 constituting theupper layer of the third hard mask removed through the fifth step, as avariation. If the sixth step is executed while at least part of the SiONlayer 216 is still present, the first hard mask is not etched readilyduring the sixth step. As a result, an advantage of minimizing theextent of shoulder sag at the via holes formed at the SiLK™ layer 206 isachieved in this case, in addition to the advantages discussed above.

The following is an explanation of the steps executed to form a dualdamascene structure in the second embodiment of the present invention byusing the etching apparatus shown in FIG. 1, given in reference to FIGS.4 and 5. As shown in FIG. 4A, an FSG layer 204 is formed as an inorganiclow-k film (with a film thickness of 500 nm) constituted of a layerinsulating film on top of an SiN layer 202 (with a film thickness of 50nm) as a protective film. Over the FSG layer 204, a SiLK™ layer 206(with a film thickness of 400 nm) is formed as an organic low-k film.Over the SiLK™ layer 206, an SiON layer 308 (with a film thickness of200 nm) constituting a first hard mask is formed as a hard mask layer tobe used to form trenches and vias and, over the hard mask layers, aphotoresist (PR) layer 212 having a pattern to be used for trenchformation is formed.

First, as shown in FIG. 4B, the SiON layer 308 constituting the firsthard mask is partially etched and a trench pattern is formed through aspecific lithography process executed by using the photoresist (PR)layer 212 for trench formation (first step). The etching conditionsunder which this step is executed include, for instance, the pressure ofthe atmosphere within the processing chamber set to 50 mT, the level ofthe power applied to the electrodes set to 500 W and the flow rates ofthe individual gases CH₂F₂, N₂ and Ar constituting the mixed gas set to20 sccm, 100 sccm and 100 sccm respectively.

After the remaining photoresist (PR) layer 214 is removed throughashing, a second hard mask is formed over the trench pattern constitutedof the first hard mask (second step) as shown in FIG. 4C. In thisembodiment, the second hard mask is a thin film constituted of an SiONlayer 316 (with a film thickness of less than 10 nm). Then, as shown inFIG. 4D, a photoresist (PR) layer 218 for via formation is formed overthe second hard mask. Even if the SiLK™ layer 206 has become exposedduring the first step due to over-etching of part of the first hardmask, the second hard mask constituted of the same material as thematerial constituting the first hard mask is formed over the first hardmask in the second step to cover the SiLK™ layer 206 having becomeexposed again. As a result, an advantage is achieved in that the SiLKand the resist are not allowed to become mixed with each other.

Next, as shown FIG. 4E, the SiON layer 316 constituting the second hardmask and the remaining SiON layer 308 constituting the first hard maskare etched through a specific lithographic process executed by using thephotoresist (PR) layer 218 for via formation and thus, a via pattern isformed (third step).

Then, by using the via hard mask constituted of the second hard mask andthe first hard mask which have been formed through the third step, theSILK™ layer 206 constituted of an organic low-k film is etched and viasare formed at the SiLK™ layer 206 and the photoresist (PR) layer 218 isremoved through ashing, as shown in FIG. 4F (fourth step). This step isexecuted under etching conditions which include, for instance, thepressure of the atmosphere within the processing chamber set to 100 mT,the level of the power applied to the electrodes set to 1000 W and theflow rates of N₂ and H₂ constituting the mixed gas set to 100 sccm and300 sccm respectively. After the photoresist (PR) layer 218 is removedduring the step, shoulder sag may occur at the exposed second hard maskdue to over-etching.

Accordingly, the SiON layer 316 constituting the second hard mask wherethe shoulder sag has occurred is removed (fifth step), as shown in FIG.5A. During this step, the SiON layer 316 constituting the second hardmask is removed and also, the via pattern portion of the SiON layer 308constituting the first hard mask is etched to form a trench pattern.

Next, as shown in FIG. 5B, vias are formed at the FSG layer 204 by usingthe vias formed at the SiLK™ layer 206 constituted of an organic low-kfilm as a via pattern (sixth step). The etching conditions include, forinstance, the pressure of the atmosphere within the processing chamberset to 45 mT, the level of the power applied to the electrodes set to1500 W and the flow rates of the C₄F₈, CO and Ar constituting the mixedgas set to 12 sccm, 225 sccm and 400 sccm respectively.

Then, as shown in FIG. 5C, a trench pattern is formed at the SiLK™ layer206 by using the trench pattern at the SiON layer 308 constituting thefirst hard mask (seventh step).

Next, as shown in FIG. 5D, the SiN layer 202 is etched by using the viapattern at the FSG layer 204 to achieve a through via hole. This processshould be executed under etching conditions which include, for instance,the pressure of the atmosphere within the processing chamber set to 30mT, the level of the power applied to the electrodes set to 500 W andthe flow rates of CH₂F₂, O₂ and Ar constituting the mixed gas set to 20sccm, 20 sccm and 100 sccm respectively. Through the steps describedabove, a dual damascene structure having trenches and vias formedsimultaneously therein is completed. Then, a wiring step is completed byembedding Cu or a metal containing Cu (not shown) in the trenches andthe vias.

As explained above, the second hard mask formed as a dummy film which isnot allowed to remain in the finished dual damascene structure is placedover the trench pattern at the first hard mask in the embodiment. Thus,the second hard mask functions as a protective film for the first hardmask halfway through the process to minimize the extent of shoulder sagat the first hard mask. This advantage will prove even more effectiveunder circumstances in which the adverse effect of shoulder sag is moresignificant in the related art, i.e., when the trench width isapproximately 0.18 μm or smaller and the via diameter is approximately0.13 μm or smaller. In addition, since the first hard mask and thesecond hard mask are constituted of the same material, an advantage isachieved in that the SiLK and the resist are not allowed to become mixedwith each other even if the SiLK™ layer 206 becomes exposed due toover-etching of part of the first hard mask during the first step.Furthermore, since the SiON constituting the second hard mask alsofunctions as a reflection-reducing film, there is an added advantage ofsustaining dimensional stability during the lithography process.

It is to be noted that the following method may be adopted as avariation. In the fifth step, the SiON layer 316 constituting the secondhard mask is not removed, and the SiON layer 316 is also left unetchedduring the etching process executed for the via formation at the FSGlayer 204 in the sixth step. Then, through via holes are formed byetching the SiN layer 202. When the etching process is completed, theSiON layer 316 is removed through isotropic etching, and then the SiONlayer 308 remaining at the trench portion is removed through asubsequent anisotropic etched-back process. In this case, the lowermostSiN layer 202 can be etched while the SiON layer 308 is still present atthe trench portion and since SiON demonstrates a higher selection ratiothan SiLK™ during the process of etching the SiN layer, an advantage isachieved in that the extent of shoulder sag at the top of the opening ofthe via hole, which occurs during the state corresponding to FIG. 5Cthrough FIG. 5D in the method described earlier is minimized.

While the invention has been particularly shown and described withrespect to preferred embodiments thereof by referring to the attacheddrawings, the present invention is not limited to these examples and itwill be understood by those skilled in the art that various changes inform and detail may be made therein without departing from the spirit,scope and teaching of the invention.

For instance, while an explanation is given above on examples in whichthe etching methods achieved in the embodiments are adopted in theplasma etching apparatus shown in FIG. 1, the present invention is notlimited to these examples and it goes without saying that the presentinvention may be adopted in etching apparatuses that use various typesof plasma sources as well as plane parallel type etching apparatuses.

In addition, while an explanation is given above in reference to theembodiments on an example in which SiLK™ is used to constitute theorganic low-k film and FSG is used to constitute the inorganic low-kfilm, the present invention is not limited to this example. The organiclow-k film may be a polynaphthalene fluoride polymer film, a maleimidebenzocyclobutene polymer film, a polyperfluorocyclobutene aromatic etherfilm, a polyimide film, a polyallyl ether film, a Parylene film, adiamond hydride film or a polytetrafluoroethylene film. Moreover, thepresent invention may be adopted in conjunction with a divinyl siloxanebenzocyclobutene polymer film having part of its organic macro-molecularfilm replaced with silica or a polyimide film containing silica. Inaddition, the inorganic low-k film may be constituted of an SiOC film(carbon-added silicon oxide film), an HSQ (hydrogen-added silicon oxidefilm) or the like.

Also, while the first hard mask constituted of SiO₂ and the second hardmask constituted of SiON are formed as mask layers over the organiclow-k film in the first embodiment, the present invention is not limitedto this example. Of the mask layers formed over the organic low-k film,i.e., the so-called hard masks, the first hard mask may be an insulatingfilm such as a silicon nitride film (SiN), a silicon carbide film (SiC),a porous silicon nitride film, a silicon oxide nitride film (SiON), analuminum nitride film (AlN) or a silica film as well as a silicon oxidefilm (SiO₂). Alternatively, it may be constituted of a metal nitridefilm such as titanium nitride (TiN) or tantalum nitride (TaN), or atitanium carbide film (TiC). However, when a conductive nitride filmsuch as a TiN film or a TaN film is used, it is necessary to remove theconductive nitride film by polishing it off through chemical machiningor through dry-etching after copper is embedded in the wiring groovesand the vias. In addition, the second hard mask may be constituted byusing an insulating film such as a silicon oxide film (SiO₂), a siliconnitride film (SiN), a porous silica film or a silicon carbide film aswell as SiON. It may instead be constituted with a metal nitride filmsuch as titanium nitride (TiN) or tantalum nitride (TaN), or it may beformed of titanium carbide (TiC). The crucial point that should be keptin mind when selecting materials to constitute the hard masks is thatdifferent materials should be selected to constitute the first hard maskand the second hard mask.

Moreover, while through via holes are formed at the SiN layer 202 afterthe trench pattern is formed at the SiLK™ layer 206 in the seventh stepin the two embodiments described above, the present invention is notlimited to this example. The trench pattern may be formed at the SiLK™layer 206 after through via holes are formed at the SiN layer 202,instead. In addition, the etching conditions and the film thicknessesare not limited to the specific examples used in the embodiments,either.

As described above, in the etching method according to the presentinvention, a thin hard mask film (dummy film) is placed over the hardmask for trench formation in the related art for purposes of protection,and the protective dummy film is later removed, when forming a dualdamascene structure. As a result, an advantage is achieved in that theextent of shoulder sag at the hard mask for trench formation, whichbecomes exposed during the processing in the related art is lessened.Thus, the shoulder of the hard mask achieves substantial verticality, ashape that is ideal, which enables the formation of a desired wiringstructure.

1. An etching method for achieving a dual damascene structure by usingat least one layer of a low-k film and at least one layer of a hardmask, wherein: said at least one layer of said hard mask is patterned; atwo-layer dummy film, the entirety of which will ultimately be removedfrom said dual damascene structure, including a first layer formed overand in contact with said patterned hard mask and a second layer entirelyformed over and in contact with said first layer in order to preventshoulder sag; and said patterned hard mask and said dummy film includefilms constituted of a same material.
 2. The etching method forachieving said dual damascene structure according to claim 1, wherein:said low-k film is constituted with two different types of films thatare etched by using different gases.
 3. The etching method for achievingsaid dual damascene structure according to claim 2, wherein: a lowerfilm constituting said low-k film is an inorganic low-k film and anupper film constituting said low-k film is an organic low-k film.
 4. Theetching method for achieving said dual damascene structure according toclaim 1, wherein: said hard mask has a one-layer structure.
 5. Theetching method for achieving said dual damascene structure according toclaim 4, wherein: said hard mask is constituted of a silicon oxidenitride film.
 6. The etching method for achieving said dual damascenestructure according to claim 5, wherein: said dummy film is a siliconoxide nitride film.
 7. The etching method for achieving said dualdamascene structure according to claim 1, wherein: said hard mask has atwo-layer structure.
 8. The etching method for achieving said dualdamascene structure according to claim 7, wherein: at least one layer insaid hard mask is a silicon oxide nitride film.
 9. The etching methodfor achieving said dual damascene structure according to claim 8,wherein: said dummy film is a silicon oxide nitride film.
 10. An etchingmethod for achieving a dual damascene structure having vias formed at aninorganic low-k film layer and trenches formed at an organic low-k filmlayer by etching said inorganic low-k film, the organic low-k film, afirst hard mask and a second hard mask sequentially laminated on a lowerwiring layer, comprising: a first step in which a trench pattern isformed at said second hard mask through a lithography process; a secondstep in which a third hard mask is formed over the trench patternconstituted of said second hard mask; a third step in which a viapattern is formed at said third hard mask and said first hard maskthrough a lithography process; a fourth step in which vias are formed atthe organic low-k film by using the via pattern constituted of saidthird hard mask and said first hard mask; a fifth step in which saidthird hard mask is at least partially removed; a sixth step in which theremaining third hard mask layer is removed, a trench pattern is formedat said first hard mask by using the trench pattern constituted of saidsecond hard mask and vias are formed at said inorganic low-k film byusing the vias formed at the organic low-k film as a via pattern withoutaltering etching conditions; and a seventh step in which trenches areformed at the organic low-k film by using the trench pattern constitutedof said first hard mask and said second hard mask.
 11. The etchingmethod for achieving said dual damascene structure according to claim10, wherein: said third mask is a dummy film that will ultimately beremoved from said dual damascene structure.
 12. The etching method forachieving said dual damascene structure according to claim 11, wherein:said third hard mask has a multilayer structure.
 13. The etching methodfor achieving said dual damascene structure according to claim 12,wherein: an upper layer of said third mask is removed in said fifth stepand a lower layer of said third hard mask is removed in said sixth step.14. The etching method for achieving said dual damascene structureaccording to claim 13, wherein: said upper layer of said third hard maskis constituted of a silicon oxide nitride film and said lower layer ofsaid third hard mask is constituted of a silicon oxide film.
 15. Anetching method for achieving a dual damascene structure having viasformed at an inorganic low-k film layer and trenches formed at anorganic low-k film layer by etching said inorganic low-k film, theorganic low-k film, a first hard mask and a second hard masksequentially laminated on a lower wiring layer, comprising: a first stepin which a trench pattern is formed at said second hard mask through alithography process; a second step in which a third hard mask is formedover the trench pattern constituted of said second hard mask; a thirdstep in which a via pattern is formed at said third hard mask and saidfirst hard mask through a lithography process; a fourth step in whichvias are formed at the organic low-k film by using the via patternconstituted of said third hard mask and said first hard mask; a fifthstep in which said third hard mask is removed, a trench pattern isformed at said first hard mask by using the trench pattern constitutedof said second hard mask and vias are formed at said inorganic low-kfilm by using the vias formed at the organic low-k film as a via patternwithout altering etching conditions; and a sixth step in which trenchesare formed at the organic low-k film by using the trench patternconstituted of said first hard mask and said second hard mask.
 16. Theetching method for achieving said dual damascene structure according toclaim 15, wherein: said third hard mask is a dummy film that willultimately be removed from said dual damascene structure.
 17. Theetching method for achieving said dual damascene structure according toclaim 16, wherein: said third hard mask has a multilayer structure. 18.An etching method for achieving a dual damascene structure having viasformed at an inorganic low-k film layer and trenches formed at anorganic low-k film layer by etching said inorganic low-k film, theorganic low-k film and a first hard mask sequentially laminated on alower wiring layer, comprising: a first step in which a trench patternis formed at part of said first hard mask through a lithography process;a second step in which a second hard mask is formed over the trenchpattern at said first hard mask; a third step in which a via pattern isformed at the remaining first hard mask and said second hard maskthrough a lithography process; a fourth step in which vias are formed atthe organic low-k film by using the via pattern constituted of saidfirst hard mask and said second hard mask; a fifth step in which atrench pattern is formed by removing said second hard mask and etchingthe trench pattern portion of said first hard mask; a sixth step inwhich vias are formed at said inorganic low-k film by using the viasformed at the organic low-k film as a via pattern; and a seventh step inwhich trenches are formed at the organic low-k film by using the trenchpattern constituted of said first hard mask.
 19. The etching method forachieving said dual damascene structure according to claim 18, wherein:said second hard mask is a dummy film that will ultimately be removedfrom said dual damascene structure.
 20. The etching method for achievingsaid dual damascene structure according to claim 19, wherein: said firsthard mask and said second hard mask are constituted of a same material.21. The etching method for achieving said dual damascene structureaccording to claim 20, wherein: said material is a silicon oxide nitridefilm.
 22. An etching method for achieving a dual damascene structurehaving vias formed at an inorganic low-k film layer and trenches formedat an organic low-k film layer by etching said inorganic low-k film, theorganic low-k film and a first hard mask sequentially laminated on alower wiring layer, comprising: a first step in which a trench patternis formed at part of said first hard mask through a lithography process;a second step in which a second hard mask is formed over the trenchpattern at said first hard mask; a third step in which a via pattern isformed at the remaining first hard mask and said second hard maskthrough a lithography process; a fourth step in which vias are formed atthe organic low-k film by using the via pattern constituted of saidfirst hard mask and said second hard mask; a fifth step in which viasare formed at the inorganic low-k film by using the vias formed at theorganic low-k film as a via pattern; a sixth step in which said secondhard mask is removed; a seventh step in which a trench pattern is formedby etching the trench pattern portion of said first hard mask; and aneighth step in which trenches are formed at the organic low-k film byusing the trench pattern constituted of said first hard mask.
 23. Theetching method for achieving said dual damascene structure according toclaim 22, wherein: said second hard mask is a dummy film that willultimately be removed from said dual damascene structure.
 24. Theetching method for achieving said dual damascene structure according toclaim 23, wherein: said first hard mask and said second hard mask areconstituted of a same material.
 25. The etching method for achievingsaid dual damascene structure according to claim 24, wherein: saidmaterial is a silicon oxide nitride film.